This invention relates to templates for use sub-sea, that is to say at or adjacent the bottom of the sea or other body of water and intended to provide guides for the drilling of sub-sea wells for petroleum or other liquid or gaseous hydrocarbons and also to provide, preferably, a sub-sea frame for a manifold and other means by which hydrocarbons are extracted from the wells and hydraulic and other control lines are connected to the wellhead.
It is customary to provide a wellhead template in the form of a rigid frame which includes several spaced-apart guides for drilling pipes. Such a template is deposited on or adjacent the sea bed in a desired location, with or without the aid of ancillary supports, and acts as at least an initial guide for drilling strings for up to the number of wells that can be be positionally defined by the template. It is customary for the multi-well template to support, during the extraction or production phase manifolds, xe2x80x98Christmas treesxe2x80x99 and other known equipment employed for the extraction of the liquid or gaseous hydrocarbons and the control of the process of extraction.
Known rigid templates as described in the foregoing exhibit several practical disadvantages. For example it is preferable to lower the template to the sea bed through an aperture in a drilling vessel known as a moonpool. Although moonpools are substantial in size, being typically rectangular of the order of 5 or 6 meters in breadth and 6 or 7 meters in length, they are, necessarily, limited in extent. On the other hand, it is often desirable to provide an inter-well spacing which should require, typically, a four-well template to be of the order of 20 meters by 20 meters. Although these figures are given only as typical examples, there is in any event a practical limitation on the size of a rigid template which can be deployed through a moonpool.
It is known to provide a multi-well template comprising relatively hinged parts so that the template can be deployed through the moonpool in a folded configuration and be subsequently unfolded to lie flat on or adjacent the sea bed. However, not a great increase in lateral extent can be achieved using a hinged template and deployment of it is inconvenient.
A further disadvantage of both rigid and hinged templates is their occupancy of space between the positions of the well. It is often desirable to provide additional satellite wells in the vicinity of the original drilling and it may be desirable to dispose those wells within a region generally bounded by the wells of the original template. However, with known rigid or hinged templates all subsidiary or subsequent wells must be disposed outside the general area of the template and there is therefore not only a constraint on the positioning of satellite wells but added complexity or difficulty in establishing fluid connections between the template manifold and the satellite wells.
It is known from GB-A-2003532 to provided a well template which has two xe2x80x98scissorxe2x80x99 arms each having a well guide at each end. The template is intended to float in a splayed condition.
The object of the invention is to provide an improved multi-well template. Although, as will be apparent the invention is more broadly defined hereinafter, a preferred drilling and production template for sub-sea wells in accordance with the invention comprises a plurality of individual limbs each comprising a hub connected by an arm to a drilling guide. The hub may be at one end of the arm and the drilling guide may be at the other end of the arm. The hubs or central supports are preferably of differing diameters so that they fit one within another in a xe2x80x98telescopicxe2x80x99 manner. The hubs have mutually engaging parts, preferably in the form of cut-outs or axial slots, which can accommodate the arms of other sections when they are installed. Such a template may be deployed onto a foundation from a drilling vessel with the limbs in a closed configuration and in particular with the arms stacked vertically above each other. In such a configuration the assembly may pass through the moonpool of the drilling vessel or platform. The assembly of limbs may be installed on a mechanical running tool attached to a drilling string. After the assembly lands on an appropriate foundation, the drilling string may be rotated to cause the running tool to rotate the limbs so that they fan out into a desired open configuration. The template preferable as indicated includes indexing slots which operate as the arms fan out so as to fix the arms in predetermined angular positions relative to each other. In particular, the slots ma be arranged so that as each arm is rotated relative to its neighbour it can enter the slot in the neighbour and close axially relative to the neighbour. Preferably the cut-outs or slots are arranged so that the hubs telescope into each other to provide the template with a configuration in which the arms radiate in approximately the same common plane. After the wells are drilled a suitable manifold may be installed on the centre of the structure.
Particular examples of the invention will be described in the following, with reference to the drawings.